An examination of the extinction threat faced by frogs, which have hopped on Earth for some 250 million years and are a crucial cog in the ecosystem. Scientists believe they've pinpointed a cause for the loss of many of the amphibians: the chytrid fungus, which flourishes in high altitudes. Unfortunately, they don't know how to combat it. Included: an isolated forest in Panama that has yet to be touched by the fungus, thus enabling frogs to live and thrive as they have for eons.

• Allison Argo